1. Field of the Invention
This invention concerns a novel photopolymerizable composition. More specifically, it relates to a photopolymerizable composition having excellent storage stability, with less coloration and capable of obtaining cured products having high mechanical performance.
2. Background of the Prior Art
Photopolymerization has been utilized in a wide variety of applications such as for image formation in fine fabrication processes, for example, for print materials, photosensitive agents for reproduction, printed wirings, IC and shadow masks; as well as for paints, printing inks, adhesives and the likes.
Polymerization has also been utilized in the dental art, for example, photopolymerizable compositions have been used for the production of tooth filler (composite resin, etc), tooth sealing material and dental adhesives, as well as for the production of carious tooth preventive fillers, tooth crowns and denture.
As the photopolymerizable compositions having been utilized heretofore as described above, Japanese Patent Publication No. 10986/1979, for instance, describes a photopolymerizable composition capable of curing under the irradiation of visible light or ultraviolet light and having a specific composition. The photopolymerizable composition comprises a photoinitiator complex of photosensitive agent/reducing agent, that is, a photosensitive catalyst composed of (a) at least one photosensitive agent represented by the following general formula: ##STR1## where X represents C.dbd.O, CR.sub.1 'R.sub.2 ' or CR.sub.3 'OR.sub.4 ', R.sub.1 '-R.sub.4 ' which may be identical or different with each other represent individually hydrogen or a hydrocarbon group, n is 0 or 1, the groups A which may be identical or different with each other represent individually substituted or non-substituted hydrocarbon groups, in which both of the groups A may be coupled directly or joined together by way of a bivalent hydrocarbon group, or both of the groups A may form together a condensated aromatic ring, and the group A is substituted or nonsubstituted aromatic group when n is 1 and X represents CR.sub.1 'R.sub.2 ' or when n is 0, (b) at least one reducing agent represented by the following general formula: ##STR2## where the units R which may be identical or different with each other represent individually hydrogen, substituted or non-substituted hydrocarbon groups or two units R may form a ring together with N, provided that three units R are not simultaneously substituted hydrocarbon groups, and N is not directly coupled to the aromatic group, and (c) a polymerizable ethylenic unsaturated material. Specific examples of particularly preferred,photosensitive agents can include biacetyl, benzil, benzophenone, camphor quinone, etc. As the reducing agent, there are described trimethyl amine, tripropylamine, dimethylamine, propylamine, N,N'-dimethylaniline, N-methyldiphenylamine, ethylenediamine, hexamethylenediamine, dimethylaminoethyl methacrylate, piperidine and the like. Although the materials using these photoinitiators can provide rapid curing under photoirradiation, there have been serious practical problems in that curing products suffer from remarkable coloration (mostly yellowing), significant aging change of the color under sunlight and in water, and inhibit inferior strength. Further, the composition has an extremely low storage stability under heat and circumstantial light (natural light) and resulting spontaneous curing.